[visitors] Add visitors that add more components inside a `ProgramNode`

[lorisleiva]

It would be useful to have visitors such as addAccountsVisitor, addInstructionsVisitor, addDefinedTypesVisitor, addErrorsVisitor, etc.

By default these visitors would add the provided nodes to the main program of the RootNode.

// Example.
codama.update(
  addDefinedTypesVisitor([
    definedTypeNode({ name: 'slot', type: numberTypeNode('u64') }),
    definedTypeNode({ name: 'hash', type: publicKeyTypeNode() })
  ])
);

However, we could also support an additional signature that would look for the correct ProgramNode using the provided program name.

// Example.
codama.update(
  addDefinedTypesVisitor('someAdditionalProgram', [
    definedTypeNode({ name: 'slot', type: numberTypeNode('u64') }),
    definedTypeNode({ name: 'hash', type: publicKeyTypeNode() })
  ])
);